A drip irrigation emitter receives water at relatively high line pressure and provides a drip or trickle output for irrigation purposes. Emitters are commonly inserted through the wall of a hose which supplies the water at line pressure. Some emitters are pressure compensating in that they provide a relatively constant output regardless of fluctuations in line pressure at the inlet.
To achieve drip or trickle flow, an emitter typically conducts the water from the inlet through an energy dissipating flow path such as a tortuous flow path of relatively small cross-sectional area and/or through one or more orifices of small cross-sectional area. The small cross-sectional areas are useful in reducing the pressure of the water so that a drip or trickle output is obtained.
One problem with emitters is that the small cross-sectional area through which the irrigation fluid must flow tends to trap debris and particulates, and this can clog the emitter and make it ineffective for irrigation. To address this problem, it is known to provide a relatively large or flush flow through the emitter when the water is first turned on. Some emitters provide flush flow both at the start and end of the irrigation cycle. To accomplish flush flow, the emitter is constructed so that the flow path through it is of larger cross-sectional area at the beginning of the irrigation cycle and this allows the flush flow to wash debris and particulates through the emitter and the outlet of the emitter.
One problem with providing flush flow at the start up of the irrigation cycle is that the irrigation system must be sized to supply a relatively large initial "spike" flow rate and this increases the cost for system components such as pumps, filters, piping and valves. If the system is not designed for this large spike flow, the differential pressure necessary to cause the emitter to create the relatively small cross-sectional areas needed for drip flow may not occur.
Emitters commonly employ an elastomeric disc and a flow channel in the housing against which the disc is moved by differential pressure across the disc to create the small cross-sectional areas required for a drip flow. The differential pressure is created by the flow of water through a flow passage through or around the disc. Initial spike flow can be reduced or eliminated by using a flow passage of small cross sectional area but this increases the likelihood that the flow passage will become plugged with debris or particulates. On the other hand, a flow passage of larger cross section area may not generate the needed differential pressure across the elastomeric disc to create the small cross-sectional areas needed for drip irrigation.